Thermionic amplifier



Nov. 22, l1938. D, L. PLAlsTowE l THERMIONIC AMPLIFIER Original Filed April 4, 1933 l I I I l I l I I I I l I I l I I I I I l I l .Il IIIllIIl ||\Il|| llll..

Patented Nov. 22, 1938 UNITED STATES PATENT OFFICE assignor to Radio Corp oration of America, a

corporation of Delaware Application April 4, V1963, Serial No. 664,356. Re-

, newed March 24, 1936. In Great Britain April sociated `witha preceding plurality of amplifiers, l the total output from said preceding ampliiiers beingrequired tobe amplified by the common stage.

It is often required to couple two or more stages of amplification to al succeeding common stage; for example, this requirement frequently arises in microphone pick-up systems wherein each microphone has its individual amplifier, the outputs from the individual amplifiers being 4required to be fed to a common amplier. An-

other example arises in television systems wherein each of a plurality of photo-electric cell systems has its individual photo-cell amplier whosev outputs are required -to be fed to-a main linefamplier. Arrangements of this kind present considerable practical difliculties for, if the outputs from the various .amplifiers are simply coupled in parallel to the input of the succeeding common amplifier (as is usual at the present time) trouble will be experienced unless careful matching of the phase of the outputs from the various individual amplifiers (which are coupled to the common ampliiier) is resorted to. Furthermore, since the various individual ampliers are coupled to the common amplifier input circuit in parallel the over-all gain is not very great.`

'Ihe `present invention has for its object to avoid these difficulties and according to the said invention the various individual ampliers whose total output is required to be amplified in a common succeeding stage areV connected in series with one another across an input circuit in or coupled to said common stage.

One form of construction in accordance with the invention and wherein the said invention is applied to a system comprising two ampliiiers whose total output is required to be fed to a common stage will now be described.

'Ihe invention is illustrated in the accompanyingdrawing which shows diagrammatically one form of construction in accordance therewith.

Referring to the drawing two signal inputs derived, for example, from two microphones are applied to two separate and distinct amplifiers which may be of any known type and which are represented in the accompanying drawing as within the rectangle A1 and A2 respectively, the inputs to these amplifiers being applied as indicated by the .arrows marked l and 2 respectively. The output fromnthe ampliliers A1 and A2 are applied to the input circuits of two triodes V1 and V2 respectively, these triodes being illustrated as of the indirectly heated cathode type. The triodes V1 and V2 are the ampliers whose total output is required to be ampliiied in a common succeeding stage and as will be seen `the two valves V1 and V2 are in series with a source of plate potential `(not shown). The `positive terminal +HT of the source (not shown) of plate potential is connected through an anode resistance AR to the anode of one Valve V1 the cathode of which is directlyconnected to the anode of the other valve V2 the cathode of the last mentioned valve being connected to earth. As will be seen, separate inputs are applied across the grid circuits of these two valves as 'in `the usual way, and grid resistances GRi or GRz are connected as shown between each grid and a suitable source of bias potentials B1 Aor B2. The junction point of the anode resistance and 'the anode to which said resistance is directly connected, is connected through a coupling condenser as shown to the rst grid of a` common amplifier indicated within the rectangle Ci.

The invention is of course not limited to arrangements wherein'inter-stage coupling is eifected vas illustrated by resistance and capacity but other forms of coupling may be employed.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed,` I declare that what I claim is: i

l. An amplifying system comprising a source ofpotentials to be amplied, a first amplifier therefor, means including a condenser for capac-` itively coupling said sourcev to the input side of said amplifier, a second source of potentials to be amplified, a second amplifier, means includinga condenser for capacitively coupling-said second source to the input side oi said second amplifier, a tube having an input grid, a' cathode and a plate, means including a condenser ier capacitively coupling the output ci" the first ampliiier to the input grid and cathode of `said tube, another tube having an input grid, a cathode and a plate, means including a condenser for capacitively coupling the output of said second amplilier to the input grid and cathode of other tube, means for directlyconnecting the cathode of one of said tubes in series with tiepiateof the other of said tubes, a connection supplying plate potential to said tube whose cathode is connected serially withthe plate of the other tube, whereby plate potential for `said other tube is supplied through said serial' connection, a common amplifier for said tubes, means connecting the input terminals of said common amplifier across the plate of one of said tubes and the cathode of the other of said tubes, and an output circuit connected to the output terminals of said common amplifier.

2. In an amplifier circuit system wherein the total output of a plurality of amplifiers receiving separate inputs is required to be amplified in a common succeeding amplifier, said circuit system comprising, a plurality of separate input sources, a separate amplifier having a plurality of thermionic tubes connected to each separate input source, means for combining the output of said separate amplifiers comprising a first and second thermionic amplifier device having at l least an anode, grid and cathode, each one of said thermionic amplifier devices being coupled to said separate input sources by separate capacitive means connected from the output of each of said separate amplifiers to the grid of the respective thermionic amplifier device, said thermionic amplifier devices being connected in series by a connection from the cathode of said first thermionic device to the anode of said second thermionic device, the output of said first and second thermionic devices being connected across the input circuit of the co-mmon succeeding amplifier.

' 3. In an amplifier circuit system wherein the total output of a plurality of amplifiers receiving separate inputs is required to be amplified in a common succeeding amplifier, said circuit system comprising, a plurality of separate input sources, a separate amplifier having a plurality of thermionic tubes connected to each separate input source, means for combining the output of said separate amplifiers comprising a first and a second thermionic amplifier device each having at least an anode, grid and cathode electrode, capacitive coupling means connecting the output of said separate amplifiers to the grids of said first and second thermionic amplifier devices, an anode resistance connected from the anode of said first thermionic amplifier device to the positive side of a high potential source, the cathode of said first thermionic amplifier device being connected to the anode of said second thermionic amplifier device, the cathode of said second thermionic device being connected tothe negative side of said high potential device, and a coupling condenser connected to the junction point of said anode resistance and said anode for coupling said first and second thermionic devices to the input grid circuit of said common succeeding amplifienvthe cathode of said common succeeding amplifier being connected to the negative side of said high potential source. 4. An amplifying system comprising a source of potentials to be amplified, a first amplifier therefor, means including a condenser coupling said source to the input side of said amplifier, a second source of potentials to be amplified, a second amplifier, means including a condenser for capacitively coupling said second source to the input side of said second amplifier, a vacuum tube having an input grid, a cathode, a separate heater for indirectly heating said cathode, and a plate, means including a condenser for capacitively coupling the output of the first amplifier to the input grid and cathode of said tube, anothervacuum tube having an input grid, a cathode, a separate heater for indirectly heating said cathode, and a plate, means including a condenser for capacitively coupling the output of said second amplifier to the input grid and cathode of said other tube, means for directly connecting the cathode of one of said tubes in series with the plate of the other of said tubes, a connection supplying plate potential to said tube Whose cathode is connected serially with the plate of the other tube, whereby plate potential for said other tube is supplied through said serial connection, a common amplifler for said tubes, means connecting the input terminals of said common amplifier across the plate of one of said tubes and the cathode of the other of said tubes, and an output circuit connected to the output terminals of said common amplifier. v

5. An amplifying system comprising a source of potentials to be amplified, a. first amplifier therefor, capacitive means for coupling said source to the input side of said amplier, a second source of potentials to be amplified, a second amplifier, capacitive means for coupling said second source to the input side of said second amplifier, a vacuum tube having an input grid, a cathode, a separate heater for indirectly heating said cathode, and a plate, capacitive means for coupling the output of the first amplifier to the input -grid and cathode of said tube, another vacuum tube having an input grid, a cathode, a. separate heater for indirectly heating said cathode, and a plate, the .heaters of said first and second mentioned indirectly heated tubes being connected together in parallel from a source of electrical potential, capacitive means for coupling the output of said second amplifier to the input grid and cathode of said other tube, means for directly connecting the cathode of one of said tubes in series with the plate of the other of said tubes, a connection supplying plate potential to said tube whose cathode is connected serially with the plate of the other tube, whereby plate potential for said othertube is supplied through said serial connection, a common amplifier for said tubes, means connecting the input terminals of said common amplifier across the plate of one of said tubes and the cathode of the other of said' tubes, and an output circuit connected to the output terminals of said common amplifier.

6. In an amplifier circuit system wherein the total output of a plurality of amplifiers receiving separate inputs is required to be amplified in a common succeeding amplifier, said circuit system comprising a plurality of separate input sources, a separate amplifier having a plurality of thermionic tubes connected to each separate input source, means for combining the output of said separate amplifiers comprising a first and second thermionic amplifier device having at least an anode, grid and cathode, each one of said thermi-onic amplier devices being coupled to said separate input sources by separate capacitive means connected from the output of each of said separate amplifiers to the grid of the respective thermionic amplifier device, a separate bias resistance and a source of bias potential connected in series between each grid and cathode of said first and second thermionic amplifier devices, said thermionic amplifier devices being connected in series by a connection from the cathode of said first thermionic device to the anode of said second thermionic device, the output of said first and second thermionic devices being connected across the input circuit of the common succeeding amplifier.

'7. In an amplifier circuit system wherein the total output of a plurality of amplifiers receiving separate inputs is required to be amplified in a common succeeding amplier, said circuit system comprising a plurality of separate input sources, a separate amplier having a plurality of thermionic tubes connected to each separate input source, means for combining the output of said separate amplifiers' comprising a first and a second thermionic amplifier device each having at least an anode, grid and cathode electrode, capacitive coupling means connecting the output of said separate ampliers to the grids of said first and second thermionic amplifier devices, a separate bias resistance and a source of bias potential connected in series between each grid and cathode of said rst and second thermionic amplifier device, an anode resistance con- 3 nected from the anode of said rst thermionic amplifier device to the positive side of a high potential source, the cathode of said rst thermionic amplifier device being connected to the anode of said second thermionic amplier device, the cathode of said second thermionic device being connected to the negative side of said high potential device, and a coupling condenser connected to the junction point of said anode resistance and said anode for coupling said first and second thermionic devices to the input grid circuit of said common succeeding amplifier, the cathode of said common succeeding amplifier being connected to the negative side of said high potential source.

DONALD LEOPOLD PLAISTOWE. 

